1. The Field of the Invention
The present invention relates to wireless radio receiver technology and, more specifically, to improved circuits and methods for the detection of the amplitude of baseband signals.
2. Background and Related Art
Electrical signals have proven to be an effective means of conveying data from one location to another. However, for any given transmission medium, the further a signal is transmitted, the greater the decay in the signal and the greater the chance for irreversible loss in the data represented by the signal. In order to guard against this signal decay, the core electrical signal that represents the data (i.e., the baseband signal) may often be modulated or superimposed on a carrier wave in the Radio Frequency (RF) frequency spectrum.
If the baseband signal has been modulated, then RF receivers demodulate the baseband signal from the modulated signal. Regardless of whether or not the baseband signal was modulated on a carrier signal, the data represented by the baseband signal may then be interpreted by other downstream circuitry. In order to extract the data from the baseband signal, it often necessary to determine an amplitude of the baseband signal at particular sampling times. For example, such amplitude detection is important when the baseband signal is encoded using Amplitude Shift Keyed (ASK) encoding, On-Off Keyed (OOK) encoding, or another amplitude-based encoding technique.
One important parameter for amplitude baseband detection is called xe2x80x9cdynamic rangexe2x80x9d, which is the ratio of the highest detectable amplitude in decibels to the lowest detectable amplitude in decibels. A higher dynamic range is desirable since a greater range of amplitudes are detectable.
Another important parameter in amplitude detection is whether detection is performed on baseband signals that are required to be synchronously demodulated, or whether detection is performed on baseband signals that are required to be asynchronously demodulated. Synchronous demodulation means that the locally produced oscillation used to perform demodulation must be synchronized with the frequency of the carrier wave upon which the baseband signal is modulated. Such synchronization typically requires additional circuitry as compared to not having such synchronization.
Accordingly, what is desired are methods and circuits for performing amplitude detection with a high dynamic range and without regard for whether demodulation is synchronous or asynchronous.
In accordance with the present invention, methods and circuits for detecting the amplitude of an electrical signal such as a baseband electrical signal are described. The amplitude detection may be performed by performing full wave rectification on both an in-phase portion of the electrical signal, as well as on a quadrature-phase portion of the electrical signal. An output signal is then generated that is approximately proportional to the sum of the two rectified signals. For example, the output signal may be generated by summing the rectified in-phase signal and the rectified quadrature-phase signal.
In one example, the full wave rectification on the in-phase portion of the electrical signal is performed by a waveform sharpener in concert with a commutating mixer and a subtracting amplifier. The waveform sharpener generates control signals in the form of square waves. One control signal is high when the corresponding in-phase portion of the electrical signal is high, and low when the corresponding in-phase portion of the electrical signal is low. Another control signal is high when the corresponding in-phase portion of the electrical signal is low, and low when the corresponding in-phase portion of the electrical signal is high.
The commutating mixer receives and is controlled by the control signals such that the commutating mixer passes the high portion and low portions of the electrical signals to the positive and negative terminals of the subtracting amplifier at appropriate times such that the subtracting amplifier generates a signal that represents a fill wave rectification of the in-phase portion of the electrical signal. Similar full wave rectification may occur in the quadrature-phase portion of the electrical signal.
The output signal may then be used to determine the amplitude of the input electrical signal. For example, the peak amplitude of the output signal will be proportional to the amplitude of the originally input signal. For example, if the baseband electrical signal is encoded using Amplitude Shift Keying (hereinafter also referred to as xe2x80x9cASKxe2x80x9d) or On-Off, Shift Keying (hereinafter also referred to as xe2x80x9cOOKxe2x80x9d) encoding techniques, the peak amplitude of the output signal generated by the amplitude detection circuit is relevant in identifying data represented by the signal. However, the amplitude information may also be relevant for other applications as well.
The method and circuit for amplitude detection have a number of advantages including a high dynamic range and the ability to function regardless of whether the baseband electrical signal is synchronously or asynchronously modulated. The circuit for amplitude detection described below also has a small time constant or delay, and may be constructed using current integrated circuit fabrication processes.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by the practice of the invention. The features and advantages of the invention may be realized and obtained by means of the instruments and combinations particularly pointed out in the appended claims. These and other features of the present invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth hereinafter.